1. Field of the Invention
This invention relates to guidance and control methods for automatically guided vehicle (AGV) systems such as mobile robots and more specifically to methods for directing an AGV to move at a specific speed and angle (from one fixed location to another), to methods which allow two or more AGVs to cross paths without conflict, to methods which provide on-board control of an AGV's steering and drive mechanisms, and to methods for checking, coordinating, and communicating differences between the AGV's absolute position and its calculated position.
2. Description of the Related Art
Conventional automatically guided vehicles such as those used to move materials in warehouses and factories provide minimal point-to-point movement control. Most such systems involve AGVs which follow a fixed guide track, usually either a radio transmitter antenna wire buried in the factory floor, a reflective stripe painted on the floor, or a reflective tape glued to the floor. Such methods are described in U.S. Pat. Nos. 45,300,056, 4,554,724, 4,562,653, 4,593,238, and 4,593,239. All of these schemes purposely limit the individual AGV's freedom of movement by constraining the AGVs to follow a physically fixed path.
Most such systems rely on on-vehicle proximity detection, such as active bumpers or ultrasonic sensors, to deal with collisions with other AGVs, stationary objects, or personnel. In such systems, the AGVs also may move only one direction along the track.
Systems such as those described in the related Texas Instruments applications achieve true point-to-point movement by implementing control schemes which allow multiple AGVs to coexist in the same pathways without collision or excessive queuing and by using free-roving AGVs having programmable bi-directional paths. These new methods maximize the degrees of freedom of AGV movement. The control scheme set forward in TI-11104, co-pending, implements a scheme of "static" collision avoidance for AGV systems. Essentially, that method uses a rule-based computer program to examine the "mapped environment" set forward in TI-10942, U.S. application Ser. No. 771,397 and to report only those pathways determined "passable to AGVs" to a central data base, from which another scheduling program can draw the data necessary to move AGVs from one point to another in the system without attempting to place two AGVs in the same place simultaneously.
Important disadvantages of the prior art are: it is either limited to closed pathways, unidirectional motion, lack of external control of AGV motion, or to "static" collision avoidance (i.e., path planning as opposed to path supervision).